Aquatic facilities, such as swimming pools, become contaminated from various components in the environment such as dust, bacteria, and viruses, as well as from waste products produced by the bathers. To ensure that the pools can be enjoyed safely, the pool water is treated to reduce or eliminate chemical oxygen demand (COD) and/or total organic carbon (TOC) in the water. Typically, chlorine or bromine is used to disinfect the water and prevent viruses and bacteria from being transmitted among the bathers. Halogen donor compounds such as chlorine or bromine are also used to sanitize/oxidize waste products produced by the bathers.
To achieve an effective level of antimicrobial and viricidal activity, the oxidation potential of water must be sustained above a threshold value. Sustaining the oxidation potential is an uphill battle, as the oxidation potential is continuously reduced by contaminants' consumption of the sanitizing/oxidizing agent. Studies have confirmed that the effectiveness of chlorine/bromine-based sanitizers is significantly reduced with increased contaminant level. As used herein, the “contaminant” is any substance that reacts with and consumes the sanitizing/oxidizing agent. In swimming pool and other waters, contaminants often come in the form of organic compounds.
Sanitizing water would be relatively easy if the only type of contaminants were inorganic nitrogen waste products (e.g., ammonia, ammonium), as chlorine can convert the ammonia to inert nitrogen gas using the well known breakpoint chlorination process. However, when the water also contains organic nitrogen waste products, the breakpoint chlorination process is significantly impaired. This impairment is at least partly due to the fact that organic nitrogen reacts with the sanitizing agent in a less desirable competing reaction. The competing reaction entails chlorine's reaction with the organic nitrogen to produce a volatile and irritating byproduct known as chloramine (NH2Cl, NHCl2, NCl3, R2NCl, RHNCl, where R represents organic constituent). Because some of the chlorine is turned into chloramines by the organic nitrogen (instead of being turned into inert nitrogen by the inorganic nitrogen), the ability of chlorine (or other halogen)-based sanitizing/oxidizing agent to rid the water of inorganic nitrogen such as mono- and di-chloroamines is significantly impaired.
In applications such as swimming pool water, where both organic and inorganic nitrogen are present, organic nitrogen that forms chloramines competes for chlorine against inorganic nitrogen that forms inert nitrogen. Chloramines accumulate because chlorine is consumed more readily by the organic byproducts than the already partially oxidized chloramines. Accumulation of chloramines is undesirable for a number of reasons. First, chloramines are less effective as oxidizers than chlorine. Second, incomplete oxidation of the Total Organic Carbon (TOC) by reaction with chlorine produces trihalomethane (THM), which are known carcinogens. Furthermore, chloramines and THM induce corrosion of metals and impose mild to severe irritation to bathers' eyes, skin, and respiratory systems.
To control disinfection rates and prevent the accumulation of chloramines, the organic byproducts must be effectively oxidized independently of chlorine, leaving chlorine free to react with the inorganic nitrogen. This way, the chlorine is free to disinfect the water by converting the inorganic nitrogen to inert nitrogen gas. Also, when the TOC is diminished, the potential for formation of THM by reaction between chlorine and the TOC is reduced. Thus, a method and composition for achieving breakpoint chlorination without accumulation of chloramines and formation of incomplete oxidation products is desired.